Automatic substation telephone circuit



A ril 21, 1925. .1,534,144

' A. B. SMITH AUTOMATIC SUBSTATION TELEPHONE CIRCUIT Filed June '7, 1922Patented Apr. 21, 1925'.

sere e eases: SMITH,

or EVANSTON, Lm-nors, Assistant) eufi oiirfi fio TRIO ooMPANY, on onrceeo, ILLINOIS, AfooRroRATIonor rumors.

#AUT'o'MATIo suesr'niri'on Tennyson "drawn.

*Appnea'iidn net June 7, E522. Serial m: aesjses.

To all whim 'z't Be it known that I, ARTHU Bnssnr Smith, acitizen er theUnited States of America, -and a resident of Evanston, Cook GountyfandStateof llli'noisyhave' invented certain new and useful Improvements inAutomatic Substation Telephone Circuits, of which the fol-lowing' is aspecification.

The present *inyention relates to automatic substation telephoneeireairs, and the object, briefly stated, is the provision "of new andimproved circuits foran automatic telephone substation, whereby anexisting.

manual telepho'ne having the usual three spring switch-hook combinationcan be changed into an automatic telephone by the addition ofcalling-device havingthe usual three 'spring'shnnt spring combination.

Circuits have been devised before which utilizethe standard threespring. switchhook combination on an'e'xisting manual telephone set ofthe usual booster type when the telephone is changed to an automatictelephone by the addition of a suitable called device. 'So 'far asapplicant knows, however, all the prior-substation circuits of the abovementioned type require a special calling device having two pairs ofshunt springs insulated from each other. The presentcase ditiers fromthe preceding ones in that only three shunt springs are used on thecalling device, which calling device, accordingly, may be of standardmake.

The improved circuits will now be described with reference to theaccompanying drawings comprising Figs. 1 and 2, in which Fig. 1 is asimplified diagram of the improved substation circuit, and Fig. 2 is awinding diagram of a manual desk telephone converted into an automatictelephone 7 by the addition of a. standard calling device and bysuitable changes in the Wiring to conform with the circuit shown in Fig.1.

Referring now particularly to Fig. 1, the bell B and condenser C arepermanently bridged across the line conductors 2 and 3 according to wellknown practice. hen the receiver is removed, a direct current bridge isclosed across the line conductors 2 and 3 at the switch-hook 10 andspring 11, and includes the upper winding of the induction coil 1, thetransmitter T, and springs 4: and 5 of the calling device CD.

Also, switch h' ook "10 and Contact 9 the receiver R and the' lowerwinding ozt the induction boil 1, in series with-thecondenser "G, aroundthe transmitter T.

In case the subscr iber is maleinga eaill, he operates his callingdevice GD in "the usnal inanner, and when the dial is turned from itsnormal position, shunt springs ti, 7, and 8 make contact with each otheiin the usual manner, *fsprin gs and i jxup'on coming together, sliuntthe receive r R so as "to eliminate undesirable 'cl-ieki ngt Springs 7and 8, upon coming together, shunt the transmitter Tsoas to lower -'theresistance of thelbridgeacross conductors 2 "aide. As 'the'dia-l' of thecal-lingdevi'ce rotates back to its normal: position, the bridge acrossconductors 2 and; 3 is opend the desired number of times "ats'pri-ngs"-'l and 5, and when "the normal position is reached, springs 6, 7 andS'separate; thereby removing theshunt from arou'nd"tl1e=receivcr R andthe shun't from ar Ou nd -the transmitter T.

It may occur occasionally that asribscriber, knowing thatfthe'recei'ver' must-"be removed before a call can be made, operates hiscalling device with the "receiveron the hook, thinking of course that noharm is being done. When the present substation circuit is used,however, the automatic switches are operated when the calling device isturned, regardless of whether the receiver is off the switch-hook ornot. This is due to the fact that shunt springs 6 and 7, upon cominginto engagement with each other when the calling device is turned, shuntswitch-hook 10 and spring 9, thereby closing a circuit across lineconductors 2 and 3, through the bell B and the lower winding of theinduction coil I. Then, as the calling device returns to normalposition, the bridge across the line conductors is interrupted in theusual manner. However, the subscriber is warned that he is doingsomething he should not do by the tapping of the bell B which isoperated at this time because it is not shunted by the upper winding ofthe induction coil I. The subscriber, upon hearing the tapping of thebell B, knows that he is doing something wrong and refrains from idlyoperat ing the calling device CD. Of course, the bridge across the lineconductors 2 and 3 is opened againwhen the calling device OD returns tonormalposition, and the exchange switches are again released.

Referring now to Fig. 2, which is a wiringdiagramot the substation shownin Fig.

'1,the equipment shown on the left'compris- 7 ing the bell B, thecondenser G,'the induction coil I, and the associated terminal strip,

is located in the bell box of an ordinary desk telephone and isconnected to the desk stand F bynathree conductor cord. -The equipmentin the desk stand comprises the transmitter T, receiver R, callin deviceCD, switchhook springs:9,10, an 11, and the associated terminal strip.The wiring diagram may be readily checked up with the schematic diaaninduction coil having two windings, one

of saidiwindings being in series'with one of said line conductors, acalling device having control contacts, a transmitter, said controlcontactsandsaid transmitter being connectedin series in the other ofsaid line conductors,- a receiver, a thirdconductor connected at one-endto avpointbetween said bell and said condenser, the other winding'ofsaid induction coil and said receiver connected in series in the ordernainedin said third conductor, three switch hook contacts at each ofwhich a different one of said conductors terminates, said contactsadapted to close togetherwhen said receiver is lifted, and-three shuntcontacts on said calling device adapted to close together when saiddevice is off normal, one of said shunt contacts connected to one sideof said transmitter, the second shunt contact permanently connectedtothe other side of said transmitter, and the third shunt contactconnected between said receiver and said other winding.

2. In a substation telephone circuit, two line conductors, a bell and acondenser bridged across said conductors, an induction coil having twowindings,-one of said wind ings being in series w1th one of said lineconductors, a calling device having control contacts, a transmitter,said control contacts being connected in series inthe other of said lineconductors at a point between the condenser and the said transmitter, areceiver, a third conductor connected at one end to a point between saidbell and said condenser, the other winding of said induction coil andsaid receiver connected in series in said third conductor, threeswitch-hook contacts at each of which a different one of said conductorsterminates, said contacts adapted to make contact with each other whensaid receiver is lifted, three shuntcontacts on said calling deviceadapted to make contact with each other when said device is off normal,one of saidshunt contacts permanently connected to one side of saidtransmitter, the second shunt contact permanently connected to the otherside of said transmitter,- and the third shunt contactconnected betweensaid receiver and said other winding.

In witness whereof, I hereunto subscribe my name this 31st day of May,A. D., 1922.

ARTHUR BESSEYSMITH.

